1. Field of the Invention
The present invention relates to autonegotiation controllers within the physical layer of devices that are connected to an Ethernet network. More particularly, the present invention is directed to an autonegotiation controller in which the physical layer of one network device is able to supply power to another network device, if required, over the data cable connecting the devices.
2. Description of the Related Art
FIG. 1 illustrates a network device 10 in communication with another network device 12 over cable 18. These devices are well known. Network devices include, by way of example, network switches, computers, servers, network enabled appliances and the like. Heretofore, network devices have generally required external power from an AC power source. This methodology suffers from a number of drawbacks, including requiring an external power supply, which can be costly. Accordingly, it would be desirable to implement a system in which the power for one network device 12 can be supplied from the other network device 10 via the data cable 18. This approach, however, would require a physical layer of network device 10 to determine whether a DTE device is connected to cable 18 and whether DTE device 12 requires power. The capability of supplying power over cable 18 is referred to as power on Ethernet cable or POE. In this application, the term “cable-powered DTE device” shall refer to a network device that requires power being supplied from another network device via a data cable, and the term “self-powered DTE device” shall refer to a network device in which power not supplied by the data cable. Self-powered DTE devices may be supplied by external power supplies or internal power supplies, such as, batteries. Cable-powered DTE devices generally comprise a filter to provide a return path of a test signal used in detection of the cable-powered DTE device.
In addition to detecting power, the physical layer of network device 10 also negotiates the highest common operating speed with network device 12. Referring again to FIG. 1, first and second devices 10 and 12 include physical layers 14-1 and 14-2 that are connected by a compliant cable 18 that includes four pairs of twisted pair wires (A, B, C and D). One type of compliant cable is referred to as Category 5. The physical layers 14-1 and 14-2 usually include digital signal processors (DSPs) and autonegotiation controllers (both not shown). The DSP of the first device receives and decodes signals from the second device. The DSP of the first device codes and transmits signals to the second device. The four pairs of twisted pair wires are typically labeled A (1,2), B (3, 6), C (4,5), and D (7,8). In 10BASE-T and 100BASE-TX mode, only pairs A (1,2) and B (3,6) are required to autonegotiate, to establish a link, and to communicate. In 1000BASE-T mode, however, two pairs of twisted pair wires are required to autonegotiate and four pairs are required to establish a link and to communicate.
In 10BASE-T, 100BASE-TX, and 1000BASE-T modes, the physical layer performs autonegotiation before a link is established. During autonegotiation, the devices 10 and 12 negotiate the operating speed of the link as well as other functional capabilities of the devices. A device can advertise operating speeds that are less than or equal to the maximum operating speed of the device.